The present invention relates, in general, to electrically-controlled brake systems and, more particularly, the invention relates to a setpoint adjuster for the control of such electrically-operated brake system.
As is known in the braking art, in order to control the electronic system in an electrically-controlled brake system, the pedal-operated brake valve must at least contain a sensor. Such sensor may be, for example, a slide resistance contained in the electrical circuitry. A brake valve of this kind, which is usually designed for two circuits, will generally have two built-in electric signal transmitters. A brake valve with an attached potentiometer has also been taught for use in this application.
As would be expected, particularly effective safety features are to be required for brake systems of motor vehicles. For instance, should one of the two signal transmitters break down, at least a limited braking effect must still be possible.
This same requirement is retained for the case when one of the two signal transmitters or sensors, respectively, transmits a faulty signal. As, in such a case, it may be unknown which of the two sensors has provided the erroneous signal, suitable criteria must be incorporated into the system for the detection of the signal which has broken down and for disregarding it.
The obvious solution, prior to the present invention, might be the use of three sensors, and to switch OFF the signal of the one sensor which is broken down. In this case, it is assumed that the concurring signals of the two other sensors have not broken down. This solution, however, has the disadvantage of higher expense for construction. In addition, it provides one more sensor which must be maintained, thereby adding to the overall operating cost of the vehicle.
The use of a potentiometer or displacement transducer, respectively, as an electrical component for the control of the electric brake system--which is an obvious solution known to the art--likewise has certain disadvantages. The displacement signal may scatter when the spring characteristic is changed. This would especially be the case in a cold environment. This makes sufficient repeating accuracy, under differing operational conditions, almost impossible.